Method and apparatus for the production of nonwoven fabrics



' y 1 1970, ErLuzz'AT Td 3,512,230 ME IHOD AND. APPARATUS FOR THE PRODUCTION OF NONWOVEN FABRICS Filed July 25, 1966 3,512,230 METHOD AND APPARATUS FOR THE PRODUCTION OF NONWOVEN FABRICS Ettore Luzzatto, Milan, Italy, assignor to Snia Viscosa Societa Nazionale Industria Applicazioni Viscosa S.p.A., Milan, Italy, a company of Italy Filed July 25, 1966, Ser. No. 567,638 Claims priority, application Italy, July 29, 1965, 7,536/ 65 Int. Cl. B3211 5/08; D04h 3/02; D02g 1/00 U.S. Cl. 281.2 5 Claims ABSTRACT OF THE DISCLOSURE A nonwoven fabric web is produced by extruding a plurality of tacky, closely spaced, parallel filaments downwardly from a spinneret in a common plane to a mechanical crimping device, which forms in the filaments, crimps or undulations disposed in parallel planes extending at right angles to said common plate, and ether passing the crimped filaments over a convex support surface, while simultaneously spreading the filaments apart, or depositing the filaments on a resilient moving surface which simultaneously entangles the undulations and stretches sideways to draw the entangled filaments apart.

This invention relates to a method by which textile structures and reticulated fabrics of the kind commonly called nonwoven fabrics and, more particularly, this invention is directed to a method for the production of nonwoven fabrics in the form of high-bulk webs and felts.

The invention is also concerned with the products obtained by said method and more particularly webs, felts and nonwoven fabrics in general, which aiiord as themselves a number of advantages and improvements over the nonwoven fabrics of conventional make. These advantages are particularly attendant to the resilient yieldability in any direction, softness and pliability and the uniformity of their reticulated nonwoven structure, inasmuch as there are no knots, angled spots and, in general, localized concentrations of components.

It is known that, up to now, said nonwoven fabrics are produced, in the form of felts, webs or mats, by laying down, with a regular and randomly varied orientation, relatively short staples of filamentary materials such as, generally, glass or other inorganic thermoplastic materials. Their production requires a plurality of processing steps, such as spinning, cutting the filaments into staples, projecting them and allowing them to fall with randomly variable orientations on a collecting belt on which the felt or web is formed, to be subsequently pressed and/ or bound with suitable binders.

In addition to the difficulty of their production, said prior nonwoven fabrics are exposed to a number of defects. They consist of discontinuous filaments and thus they are in any case more or less liable to a mutual sliding and dislocation. The individual filaments are present, in the fabric, along a substantially rectilinear trend and, due to their inherent inextensibility, they overcome, until they break, any tendency towards the elongation of the nonwoven fabric along the direction corresponding to their orientation. Said known nonwoven fabrics are then gradually decomposed as they are subjected to stresses and also to vibrations in different directions.

Nonwoven fabrics are also known, which consist of continuous filaments more or less randomly arranged along long tortuous paths. These fabrics require, however, clumsy and quite uncontrollable processes for their production and also very low ratios between the web production capability and the filament output, all these facts United States Pat ent 0 Patented May 19, 1970 being limitations from an economical standpoint and, moreover, their structure is such that the intersection points of the filaments are relatively few, that which puts limitations on the mechanical properties also.

It is an object of the present invention to provide a method for the production of nonwoven fabrics, which is not effected by the above listed shortcomings or by other drawbacks and limitations inherent in the conventional methods and procedures.

More particularly, it is an object of the present invention to provide a method for the production of nonwoven fabrics, starting from continuous filaments which remain such, at least the great majority, in the nonwoven fabric produced.

Another object of the invention is to provide a process for the production of nonwoven fabric whereby during the preparation of the individual filaments, said filaments are prearranged in a mutual spatial relationship with each other, so as to cause at the outset the formation of a plurality of points of contact and localized initial adhesion among said filaments, as well as a stage of laying said filaments on one or more planes, said operation giving rise to an advantageously even and regular reticulation in which the individual filaments are interlocked at a plurality of points, these latter, in turn, being advantageously and regularly distributed throughout the whole Width of the reticulation.

A complementary object of this invention is to provide a production method affording, in combination with the above listed technical effects and advantages, the advantageous feature of permitting an economy in production means and implementations.

According to a further feature of the invention, the subject process can be commercially applied by employing production means and apparatus which are continuously operable so that the production run may take place at a high speed as an uninterrupted sequence of steps, from the initial filament-formation stage to the final stage for the production of a finished fabric.

According to the invention, the method consists in producing a plurality of continuous filaments of a spinnable man-made or synthetic material by causing said filaments to be advanced over a plane and in a parallel and close side-by-side relationship, subjecting said filaments to a mechanical and, if necessary, also thermal crimping step, or to a treatment capable of imparting closely arranged undulations on the individual filaments, said undulations lying in parallel planes which are closely spaced apart and substantially perpendicular to the original planes of the filaments so that, due to the closeness of said filaments and their tendency towards being deviated from said parallel planes, the filaments come into mutual contact at a plurality of points, giving rise to adhesion phenomena which are effected or enhanced by the nature of the surface of the filaments and/or by the presence of binders and adhesives on their surfaces, and thereafter causing the mass of filaments so treated to be advanced over one or more resting surfaces on which said mass is encouraged to expand while its feeding speed is reduced. I

It has been ascertained that the spreading effect, that is the shifting apart of originally contacting filaments, and, possibly the shrinking elfect due to the decrease of their feed velocity, is conducive to a widening and extension of the undulations or a tendency towards taking up an undulated outline as caused by said crimping step, while in practice the points of mutual contact and interlock between adjacent filaments, which existed prior to laying the filament mass on said rest surfaces, and multiplied.

V In order that the above enumerated mechanical functions or" advance, spreading and shrinking in the feed direction may be obtained, a number of different technical solutions and ways of operation can be adopted, a few of which will be indicated later by way of example. It is anyhow a vital feature of the invention that, due to the laying and conveyance of the pretreated filaments on resting and feeding surfaces, the undulations of the individual filaments are laid, substantially or in a predominant manner, onthe plane defined by the rest surface, thus contributing towards the completion of the reticulated structure since the undulations 'of adjoining filaments become superposed and interlocked.

w Said mechanical treatment stages can obviously be integrated, proceeded, followed by, or alternated with, other conventional treatment stages, either mechanical or nonmechanicai, of textile filaments and yarns. For example, upstream of the crimping stage, the individual conventionally drawn filaments could-undergo setting, sizing or application of adhesives if necessary. In any case, the reticulated structure thus obtained, which is not stable, is stabilized and integrated by methods which are known in the field of nonwoven fabrics and which involve the application of adhesives and impregnation agents or the lamination with plastic sheets, a nonwoven fabric proper being obtained in the former case, and a reinforced sheet or laminate in the latter.

The nonwoven textile reticulation could also undergo other treatments such as calendering, thermal setting, finishing or other, and also, these reticulated fabrics could be placed under and laminated with other laminar components, either equal or different, for example for the formation of thicker nonwoven fabrics obtained by superposedly and intimately combining two or more webs into an elementary nonwoven fabric web, produced as aforesaid.

The foregoing and other objects, features and advantages of the invention will clearly appear from the ensuing detailed disclosure of practical non limiting examples of the subject method, as shown in the accompanying,

drawing, in which the merely constructional details of the several means, implementations and apparatus which can be used have been omitted for the sake of simplicity in that the individual components thereof can be provided according to the coventional techniques of the appertaining art.

In the accompanying drawing:

FIG. 1 is a perspective diagrammatical view of a complete installation for the production of nonwoven fabrics according to the invention and including a particularly simplified speed slackening and spreading device, and

FIGS. 2, 3 and 4 show alternative embodiments of said device in which the various parts are capable of being differently combined and used.

According to the example of FIG. 1, a plurality of filaments is produced by a conventional extruder 11 comprising a spinneret 12 whose nozzles are in alignment and closely spaced apart so that the filaments of said plurality 10 are closely adjoining to one another. Said close side-by-side relationship among the several filaments, which lie in a single plane, could, however, be obtained in the not immediate neighbourhood of the spinneret output end but somewhat distant therefrom.

The filaments of the plurality 10- could undergo conventional treatments in order to be converted into yarns or anyhow into a condition of practical utility. For example, in the case of filaments of linear synthetic polymers such as polyamides, polyesters, polyolefins, etc., these treatments will comprise one or more drawing steps such as diagrammatically shown in FIG. 1 at 13. As outlined above, there can be setting, sizing and/or application of an adhesive on the surface, and other treatments: These steps, suitably shifted, could be effected downstream of the drawing step, for example in the position shown at 14, the sequence in which said steps are performed having no criticality for this invetnic-n, but depending on the nature of the filaments and by expediency and conveniency considerations.

Said plurality of filaments 19, wherein said filaments retain said condition of coplanarity, parallelism and sideby-side relationship, is sent into and through a mechanical crimping device 15, wherefrom said plurality emerges at a given speed V and in a crimped condition as indi cated at 16. The filaments under these conditions could exhibit physically ascertainable undulations or even a mere tendency towards assuming an undulate trend. In view of the side-by-side relationship among the individual fiiaments, the crimping effect sets up a number of points of localized contact among adjacent filaments, even assuming that many points of contact might have possibly been given rise to upstream of thet crimping device 15.

The formation of said points of contact, whereat the individual filaments adhere and are initially being interlocked has, obivously, a mere casual nature on a microscopical scale and is regular only from a statistical point of view. As a matter of fact, in view of the regular relative arrangement of the filaments of the plurality 10 at the input of the crimping device 15, and also on account of the regular Way in which said conventional device mechanically acts upon filaments and yarns being fed therethrough, it has been ascertained that the points of contact are distributed, with a surprisingly advantageous statistical distribution, on the plane containing the plurality 16 of crimped filaments. These points of contact are prevailingly formed in that the filaments which, at the output of the crimping device are undulated in planes perpendicular to the plane of the plurality 16, and which are parallel and susceptible of being closely approached to one another, do not stay physically in said closely approached planes and, by being displaced, they come into mutual contact.

In order that the most favorable conditions for the formation of numerous, regularly distributed points of contact may be achieved, it is advantageous that the crimping device impart to the individual filaments unduiat-ions having an amplitude which is considerably wider than the interspace between closely adjoining filaments present in the plurality 10 at the input end of the device.

At the output end of the crimping device, the plurality of crimped filaments 16 is transferred onto at least one resting surface capable of imparting a spreading effect to said plurality, as diagrammatically shown by the arrows A, preferably associated with a reduction of the translational speed down to a value V Said action is brought about by a spreading device, generally indicated at C, which could be embodied in a number of different constructional arrangements.

For example, as depicted in FIG. 1, said device will comprise a tumbler-shaped roller 20 on whose surface the filaments are forced mutually to spread apart in a direction transverse to their direction of advance. The individual undulations are stressed by the convex surface of the roller so as to widen their amplitude and are possibly shortened when the surface speed of the roller is reduced, there being also the possibility that they assume a spirallike und-ulation.

Thus, at least in the majority of the points of mutual contact, the adherence and the mutual interlock are maintained as established at the outset. The resultant product 21 takes up and maintains in this way the characteristics of a nonwoven fabric whose reticulated pattern is surprisingly regular and anyhow exhibits the most desirable characteristics. These undulations, of course, have not a sinusoidal regular outline but tend to assume a statistical desirable trend and thus they can have sharp deviations and be arranged as skew lines within the thickness of the reticulated structure. Furthermore, each filament can have wider curves and deviations superposed to the tiny angular deviations outlined above. Moreover, the amplitude of the undulations is a small fraction of the fabrics width and could even be as small as a fraction of a millimeter, even though it is, as a rule, in the order of magnitude of a few millimeters.

The regular conveyance under the conditions of spreading and speed reduction can be assisted by encouraging the adherence of the filaments to the receiving surface, for example by employing roughened surfaces and/or surfaces provided with points, tooth-like projections or others. The spreading of the material can obviously be earned out in two stages, or more, over cascade positioned spreading devices such as the tumbler-shaped rollers 23 of F IG. 2, between which rolls 24 can possibly be interposed which, in addition to facilitating the transfer of materials from the one of the tumbler-shaped rollers 23, equalize the speed slackening of the material from the speed value V to the speed value V said rolls 24 being specially driven at different and subsequently decreasing surface velocities.

According to another embodiment of the invention, as shown FIG. 3, the crimped and adjoining filaments of the plurality 16 are laid on a conveyor belt 25 made of a resiliently extensible material, for example of rubber, borne and caused to advance for example by means of chains 26 and 27 which operate in spread out planes so as to obtain the gradual spreading of the undulated filaments which are interlocked at a plurality of points of the textile reticulation of the nonwoven fabric 21.

As exemplified in FIG. 4, the receiving and spreading surface can also be advantageously embodied so that a portion thereof undergoes a shrinking effect and a spreading effect simultaneously with respect to the direction of advance. Said surface can be, for example, formed by a conveyor belt 28 of a deformable material so that every dimensional variation in one direct-ion is conducive to an opposite dimensional variation in a direction transverse with respect to the former direction, for example a belt having a reticulated net structure and made of rubber or another material. Said conveyor belt 28 could also be mounted about capstan-shaped rollers 29 and tumbler shaped rollers 30, capable of inducing, respectively, a shrink-ing effect and a transverse spreading of the belt 28 and having a greater and a smaller surface velocity, respectively. Therefore, the material being fed over the upper lap of the belt 28 will undergo a progressive reduction of its translational speed from V to V due to the gradual shortening of the material of the belt as a function of the gradual widening thereof.

By encouraging, for example, by providing small closely arranged points, corrugations or the like, a temporary engagement between the belt surface and the overlying reticulation, the filament reticulation will be compelled to be evenly deformed, thus becoming shorter and wider, so as to assume the desired reticular structure without altering but, contrarywise, completing the mutual engagement between adjoining and superposed filaments at a great number of points of the nonwoven textile structure thus obtained.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for producing nonwoven fabrics comprising subjecting a plurality of parallel, closely adjacent and coplanar filaments to a mechanical crimping operation to impart to said filaments undulations disposed in planes substantially perpendicular to the plane of said filaments, laying said thus undulated filaments on a receiving sur face to overlap and interlock with the undulations of adjacent filaments, spreading the filaments laterally to space them apart from each other, whereby a nonwoven fabric structure is formed consisting of continuous undulated filaments, each one of which overlaps and is interlocked with at least a part of an adjacent undulated filament where their undulations cross, the filaments being spread in a plane which is transverse to the feed direction of the filaments, the spreading of the filaments being accompanied by a simultaneously shortening of the fabric, continuously advancing said receiving surface during the deposit of said filaments thereon, inducing a progressive increase in width of said receiving surface during the advance thereof, and temporarily adhering substantially every undulation of the filaments on said surface thus compelling said undulations to be concurrently widened and shrunk.

2. A method as claimed in claim 1, wherein the spreading of the filaments is accompanied by a slowing down of the rate of advance of said fabric.

3. Apparatus for the production of nonwoven fabrics, comprising means for producing a plurality of closely spaced, parallel, continuous filaments disposed in a common plane, mechanical crimping means connected to the output of said filament producing means to crimp said filaments and form therein undulations extending perpendicular to said common plane, a supporting surface engageable with the crimped filaments to displace the undulations thereof in directions which cause the undulations to overlap and interlock thereby to hold said filameans together in the form of a nonwoven fabric, said supporting surface being formed to spread said filaments laterally of one another, and said surface being formed of an extensible material which can be extended at least transverse to the direction of advance of the filaments so as to obtain a transverse spreading of said filaments.

4. Apparatus as claimed in claim 3, wherein said surface conveys and advances the filaments, from an initial speed at which said filaments reach said surface, to a lower speed at which the filaments are fed from said surface.

5. Apparatus as claimed in claim 3 wherein said surface comprises a plurality of spaced surfaces rotating at different speeds, and at least certain of said surfaces rotate, respectively, at successively decreasing speeds, to slow down the advance of the filaments concurrently with the transverse spreading of the filaments.

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